In semiconductor fabrication processes, when features in a single layer of a semiconductor device are positioned closer than patterning resolution permits, multiple masks are often used in order to pattern the features. The features of the single layer of the semiconductor device are separated into different masks so that each mask includes features which are separated by a distance equal to or greater than a patterning resolution parameter. In some instances, a process using two masks is called double patterning and a process using three masks is call triple patterning.
While designing a semiconductor device, designers will lay out the features of the semiconductor device in a layout pattern. These layout patterns include commonly used structures which are stored as standard cells in a cell library. A cell library is a database of standard cells which a designer can use in order to efficiently insert commonly used structures in a layout pattern while avoiding the extra task of designing each structure for each different semiconductor device.
In some instances, these standard cells are checked to determine whether the standard cell is colorable based on a number of masks used to form the single layer of the semiconductor device. A cell is colorable if the features of the cell are able to be separated into the number of masks with each mask maintaining a separation of the features greater than or equal to the patterning resolution parameter. For example, a standard cell which is compatible with a double patterning process is called 2-colorable, and a standard cell which is compatible with a triple patterning process is called 3-colorable.